It's not a question of them having "an interest in E&P". The point is that many G&P MLPs (like OKS) are even more exposed to commodity prices than production companies. As a processor, they produce and sell natural gas liquids. And the price of those liquids has crashed (up to 90% for some NGLs at some locations) over the last couple of months. Some G&Ps may be mostly fee based and so relatively unaffected. Others may have some hedging, however in general G&Ps are not as well hedged as E&Ps. This is partly why G&Ps crashed as much or more than E&Ps in 2008-9. Several G&Ps (for example NGLS) have already come out and stated how the crash in NGL prices is hitting their margins and distribution coverage. Anyway, we will know more about the impact to OKS soon when they release Q2 earnings.